It is well-known that a color sheet (also called color proof) for color correction is used in order to save time and labor in making galley proofs that takes place as a step prior to the production run printing in a multicolor printing process.
Since the color sheet or color proof in itself is used to estimate the color reproduction of finished prints, the color reproduction thereof must closely resemble the of final prints.
Methods for preparing multicolor transfer images by using color sheets include the direct transfer process described in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 41830/1972, wherein component colors of an image are directly transferred to be superposed on a final image-receiving paper (copying paper); the indirect transfer process described in Japanese Patent O.P.I. Publication No. 97140/1984, wherein component colors of an image are first transferred to be superposed on a provisional image-receiving sheet, and then the full color image is again transferred onto a final image-receiving sheet: and the method described in Japanese Patent O.P.I. Publication No. 501217/1981, wherein after a colored light-sensitvie layer is transferred onto an image-receiving layer, an image forming process is repeated.
In these methods, the surface of the image transfer sheet is covered with a thermoplastic organic polymer which is transferred with an image, so that the obtained image surface is too glossy to thus, giving the impression of being different from the image quality of the final prints.
The preparation of color proofs in the prior art is made in accordance with, for example, the following procedure:
As is shown in FIG. 10 (a), a colored light-sensitive sheet 81A comprising a polyethylene terephthalate (PET) film 84 having thereon in sequence a removable layer 83 and a colored light-sensitive layer 82 is used. As is shown in FIG. 10 (b), colored light-sensitive sheet 81A is contacted with a positive film original 5 as an exposure mask and exposed to ultraviolet light shown by arrows 8, and the imagewise exposed colored light-sensitive sheet is then developed to obtain an image 86 formed on image sheet 81B as shown in FIG. 10 (c). In the same manner, image sheets 81B are separately prepared for four colors; black (BK), cyan (C), magenta (M) and yellow (Y).
Where a positive image is formed from a positive original with a normal development as in the above, an o-naphthoquinonediazide compound is used as a light-sensitive compound for preparation of the image sheet.
The o-naphthoquinonediazide compound usually assumes an yellow color and has the property of becoming colorless, transparent by photodecomposition. When the o-naphthoquinonediazide compound is used as a light-sensitive material for making the above positive color proof, an area capable of becoming a colored image portion after exposure and development is the unexposed area composed of the undecomposed o-naphthoquinonediazide compound. For this reason, the color of the formed image portion appears to be black, cyan, magenta and yellow colors each tinged with the yellow color of the o-naphthoquinonediazide compound which remains undecomposed.
Since the color proof should essentially be used for the purpose of precise color correction as mentioned above, the aforementioned undesirable yellow color component needs to be removed. Therefore, after the development for the four component colors or after the image transfer, another exposure had to be made to decompose the undecomposed o-naphthoquinonediazide compound. This procedure complicates the color proof making process--particularly in the case of transferring a four color-component image. Specifically it requires a considerable exposure time to complete the decomposition of the o-naphthoquinonediazide compound in the lowest layer due to the absorption of light by pigments.
Next, in the prior art the image-formed image sheet 81B and image-receiving sheet 87 are brought into contact with each other as shown in FIG. 12B, and these sheets are heated and pressured by being passed between a pair of juxtaposed heater-built-in rollers 92 and 93 which are heated by auxiliary outer heaters 94 as shown in FIG. 12A, whereby the image on image sheet 81B is transferred onto image-receiving sheet 87. When this procedure is repeated four times to transfer four component colors onto one image-receiving sheet 87, a full color image is formed on the image-receiving sheet. In FIG. 12A, the pair of rollers 95 are transport rollers and 96 is a cooling fan. The full color image thus formed on the image-receiving sheet is then transferred by the above-mentioned apparatus onto a copy paper, whereby a color proof is prepared.
FIG. 11A-11D schematic drawings which outline of the above prior art transfer process. Prior to starting the transfer, a protective film 87c is peeled off from the image-receiving sheet 87 as shown in FIG. 11(a). The image-receiving sheet 87 comprises PET film 87a having a photopolymerizable image-receiving layer 87b coated thereon. Subsequently, the image sheet 81B of FIG. 10(c) is superposed on the photopolymerizable image-receiving layer to have its image transferred thereonto by using the transferring apparatus of FIG. 12A, and the PET film 84 is then peeled off from the image sheet 81B, as shown in FIG. 11(b). This procedure is repeated four times as stated above, whereby a full color image-receiving sheet 88 of FIG. 11(c) bearing four component color images 86 can be obtained. Then, on a copying paper 7 is superposed the image-receiving sheet 88 as shown in FIG. 11(d) to transfer the full color image 86 onto the copying paper 7 in the same manner as above, and the PET film 87a of the image-receiving sheet is peeled off. The color proof thus obtained is of a construction wherein photopolymerizable image-receiving layer 87b is present together with the full color image 86. The photopolymerizable image-receiving layer 87b, since it is viscous, is then exposed to ultraviolet rays to be polymerized for hardening.
The above hardened photopolymerizable image-receiving layer causes the aforementioned undesirable gloss of a color proof. In order to reduce the gloss, the color proof is then subjected to matting treatment, but it is still difficult to obtain an image closely resembling that of an original.
Also, any of the above-mentioned conventional methods have the disadvantage that the removability of the color image from the support is difficult. After transfer of the color image, removal of the remaining image from the support must be made very carefully, otherwise, part of the color image may, which was not transferred onto the copying paper, sometimes remain on the support.
In addition, in the transfer apparatus of FIG. 12A, in order not to have the paper or respective sheets become creased, a reinforcing plate such as a thick aluminum plate as shown in FIG. 12B is used on which are superposed the respective sheets 7 and 88 or 87 and 81B. Since a thick reinforcing plate is used in this way and the transfer is performed on a plane as shown in FIG. 12A, it is necessary to provide a pair of transport rollers 95 and 95 inside the transfer apparatus, and to provide a feeding tray 97 and receiving tray 98 outside the apparatus body. Accordingly, the apparatus' size increases, and the feeding and receiving operations are made in front and in the rear of the apparatus, so that the reinforcing plate 99 must be moved each time when one transfer operation is performed, thus causing the transfer operation to be inefficient and to take time.